Hydrocarbons are conventionally produced from a subterranean hydrocarbon-bearing formation to the surface via a well penetrating and in fluid communication with the formation. Usually, a plurality of wells are drilled into fluid communication with a subterranean hydrocarbon-bearing formation to effectively produce hydrocarbons from a particular subterranean reservoir. Approximately 20 to 30 percent of the volume of the hydrocarbons originally present within a given reservoir in a subterranean formation can be produced by the natural pressure of the formation, that is, by primary production. In the case of reservoirs which produce a low-gravity, viscous asphaltene-based crude and have no reservoir drive, that is, water or gas, or a combination of both, it is estimated that less than 5 percent of the original oil in place is produced during a primary recovery.
Thereafter, additional quantities of hydrocarbons can be produced from most subterranean formations by means of secondary recovery processes such as water or steam flooding. To accomplish secondary recovery of the hydrocarbons present in the subterranean formation, one or more wells are converted to, or drilled as, injection wells. A drive fluid such as water or steam is injected into the subterranean formation via the injection wells to drive the hydrocarbons present to one or more wells that are designated as production wells. Hydrocarbons are produced to the surface from the designated production wells by conventional production equipment and practices.
A successful secondary recovery process may result in the recovery of about 30 to 50 percent of the original hydrocarbons in place in a subterranean formation. In the case of reservoirs that produce a viscous low gravity asphaltene-based crude and have no reservoir drive, such as, water, gas, or a combination of both. Water injection has little or no effect moving this viscous oil through the subterranean formation. With regards to steam injection, higher molecular weight asphaltenes will form and precipitate because of the removal of the light weight ends which act as naturally occurring asphaltene solvents. Another problem associated with steam contacting low gravity aspaltene-based crude is that asphaltene coking will occur and plug the formation.
Tertiary recovery processes have been developed to produce additional quantities of hydrocarbons from subterranean hydrocarbon-bearing formations. Such tertiary recovery processes include the addition of a surfactant and/or a polymer to a drive fluid, such as water. A surfactant reduces the interfacial tension between formation hydrocarbons and reservoir rock, whereas a polymer, such as a polyacrylamide or a polysaccharide, increases viscosity of the drive fluid to substantially reduce fingering or channeling of the drive fluid through the formation so as to produce a more uniform injection profile that results in increased hydrocarbon recovery. In the case of reservoirs which produce a viscous low gravity asphaltene-based crude and have no reservoir drive, such as, water, gas, or a combination of both, surfactant and/or polymer injection has little to no effect on moving this viscous oil through the subterranean formation. Surfactant injection has a tendency to cause emulsion blocks in the formation reducing fluid movement through the reservoir and polymers tend to increase the viscosity of the already viscous crude also reducing fluid movement through the reservoir. With the use of surfactants and/or polymers, the fluids produced to the surface have a tendency to be heavily emulsified, such that demulsification is expensive when there are high concentrations of the crude in the water phase.
Accordingly, a need exists for a process to restore the productivity of a production well in fluid communication with a subterranean formation, the permeability of a near well bore environment being reduced by asphaltene precipitate accumulation, low gravity, viscous asphaltene-based crude produced, and lack of a reservoir drive mechanism with only gravity drainage governing fluid migration through the formation that is inexpensive and effective.
Therefore, it is an object of the present invention to provide a process for restoring the productivity of a well penetrating a subterranean formation and having an asphaltene-based precipitate accumulation in the well bore by effectively increasing the permeability of a subterranean formation.
It is another object of the present invention to provide a process for the reduction of the viscosity of low gravity asphaltene-based crude, allowing for easier migration through the subterranean formation.
It is also an object of the present invention to provide a process to establish a drive mechanism within the subterranean formation allowing the asphaltene-based crude to be produced either from the well into which fluid and gas are injected or produced from wells offset to wells into which fluid and gas are injected.
Additionally, it is an object of this invention to provide a process for restoring productivity of a well in fluid communication with a subterranean formation which is effective and relatively inexpensive.